DESTROYERS OF WEED SEEDS 89 



Professor Beal estimates the amount of weed seed 

 annually destroyed by the tree sparrow in Iowa as 

 follows: — 



On the basis of one fourth of an ounce of seed eaten 

 daily by each bird, and an average of ten birds to each 

 square mile, remaining in their winter range two hundred 

 days, there would be a total of 1,750,000 pounds, or 875 

 tons, of weed seed consumed in a single season by this one 

 species. Large as are these figures, they unquestionably 

 fall far short of the reality. 



Effect on weed-patches. Studies that have been 

 made of patches of weeds after being visited by birds 

 show that the work of destroying the seeds is done 

 very effectively by them. In April, Dr. Judd exam- 

 ined weed-patches on a farm in Maryland to see to 

 what extent the seeds had been destroyed. In one 

 field, where in the fall there had been scores of seeds 

 on every ragweed plant, it was difficult to find, during 

 a fifteen-minute search, half a dozen seeds remain- 

 ing. In another field, in a thick growth of pigeon- 

 grass, where there had been hundreds of seeds in 

 the fall, sometimes not a single one was found; and 

 on a mat of crabgrass, where there had been thou- 

 sands in the fall, frequently not one was left. 



The native sparrows are specially efficient de- 

 stroyers of weed seeds, and sometimes in two months 

 will destroy ninety per cent of the seeds of pigeon- 

 grass and ragweed. Weed seeds form more than half 

 of their food for the entire year, and during the colder 



